## Tuesday, January 1, 2013

### New Years Baby

My father in law is a New Years baby.  In fact -- he is THE new years baby for his hometown -- the first child born in 19591955. I think he has a bronze-plated baby bootie to commemorate the occasion.

I was wondering, as I always do, "What are the chances?"

Unfortunately, this question is hard to answer because it is kind of vague, so I'll try to tackle some of the different directions this question could be answered.

 Popularity of Birthdays: Darker squares are more popular birthdays than lighter Image by The Daily Viz
First, what are the chances of having a baby born on New Years?  Assuming all days are created equally, it would seem that being born on New Years would be a 1/365 chance. However, all days are not created equally. Some days are notoriously popular for delivering babies, and others particularily avoided. Christmas for instance, has very few babies born on it, but the days just prior and just after have a slightly higher likelihood. New Years is another one of those days. Of course, many pregnancies are planned and the most popular times to have children is July Aug and September, with January being one of the leas popular months to have children. This is illustrated beautifully in the info-graphic to the right.

Assuming you want to try to have the New Years Baby -- what are your chances?  This is a sticky subject because the ability to conceive a child varies so much from couple to couple, and the likelihood of a conceived child being carried healthy to full term is no sure thing either.  A few websites (#1 and #2) suggest the chance of a healthy couple conceiving in a given month are less than 20% and the chances of that baby surviving till delivery are only around 70%. While these two percentages are certainly not independent probabilities, this puts a rough likelihood of (.20*.70) or 14% chance of being able to have a baby even remotely close to New Years on purpose.

Suppose you are able to successfully conceive and even place your order on the statistically perfect date (about Day 366-281 or day 85) what are the chances you'll deliver on New Years? This is the question all pregnant women want to know -- will I have my baby on my due date?  Very unlikely. An informal survey shows only about 5% actually deliver on their due date.  Again abusing the independence of these variables, which can certainly not be assumed, 5% of 14% is 0.7%, which is only slightly higher than 1/365 chance.

Of course, even if you are able to have a child on New Year's day -- what are the chances you'll beat all the other couples trying for the bronze booties? I suppose that depends on what town you're competing in. In my hometown of Grand Rapids -- how many babies are born on a given day? Ends up this was a very hard question to answer as I couldn't find a direct answer anywhere online. A few news articles suggest to me that there are only a handful born on a given day, and so you don't necessarily have to have perfect timing, although last years new years baby did. Another website suggested only a handful of babies were born on leap day, and only a few on 12-12-12.

I couldn't find any usable birth rate statistics anywhere for Grand Rapids Michigan, but I'm not going to let that stop me. With a current population of around 190,000 and a national annual birth rate of 13.5 per 1000
that yields approximately 190,000*13.5/1000 or 2565 births per year, or about 7 births per day. Of course, hospitals in Grand Rapids service a population larger than that, but not significantly larger -- maybe double? I remember looking in the nursery at St Mary's when both of our children were born and seeing less than 10 babies there, so I'm going to say that being the first baby born on New Years add's an additional 10% chance to things, yielding a final likelihood of 0.07% or 0.0007. This seems pretty consistent with the fact that 1 of those 2565 babies born had to be the first one born in a year, and 1/2565 is .0003. I'm sure I'm grossly simplifying things here, but it looks like if want to win those bronze booties -- than try. If you try, you'll roughly double your chances of having your baby be "the new years baby" in Grand Rapids as opposed to, say, just another baby.

And that half dozen of you friends and family members who are reading this and wondering -- no, we have no intentions of winning the bronze bootie in 2014.

#### 1 comment:

1. I'm a very visual person so I love that graphic with the shaded boxes. So interesting! P.S. He was born in '55, and got a silver cup from the GR Press. ;-)